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| United States Patent |
5,681,906
|
|
Yezrielev
, et al.
|
October 28, 1997
|
Thermoset coating compositions having improved hardness
Abstract
The present invention provides for amino-crosslinkable coating formulations
based on a mixture of a di- or polyhydroxy functional polymeric component
selected from the group consisting of diesters, polyesters, alkyd
polymers, acrylic polymers and polycarbonate polymers, a crosslinking
agent such as a methylol (alkoxymethyl) amino crosslinking agent, and a
reactive additive which is the ester reaction product of a phenol
carboxylic acid, preferably para-hydroxybenzoic acid, and an epoxy
compound selected from glycidyl ethers, glycidyl esters, linear epoxies
and aromatic epoxies. The crosslinkable compositions of this invention may
be used to prepare curable coating and paint formulations, and also may
contain other ingredients such as a crosslinking catalyst, fillers,
pigments and the like. When cured, the coatings of this invention exhibit
improved physical and chemical properties when compared with cured
coatings which do not contain the ester reaction product additive.
| Inventors:
|
Yezrielev; Albert Ilya (Houston, TX);
Swarup; Vijay (Houston, TX);
Rigopoulos; Konstantinos R. (Baton Rouge, LA)
|
| Assignee:
|
Exxon Chemical Patents Inc. (Houston, TX)
|
| Appl. No.:
|
424205 |
| Filed:
|
April 19, 1995 |
| Current U.S. Class: |
525/450; 525/400; 525/408; 525/418; 525/437; 525/444; 525/451; 525/509; 525/519; 525/534 |
| Intern'l Class: |
C08L 061/20; C08L 061/28; C08L 067/00 |
| Field of Search: |
525/451,437,444,400,408,534,450,418,509,519
|
References Cited
U.S. Patent Documents
| 3409579 | Nov., 1968 | Robbins | 260/30.
|
| 3789044 | Jan., 1974 | Taft et al. | 260/18.
|
| 3836491 | Sep., 1974 | Taft et al. | 260/22.
|
| 4031068 | Jun., 1977 | Cantor | 260/79.
|
| 4130549 | Dec., 1978 | Ueno et al. | 528/93.
|
| 4331782 | May., 1982 | Linden | 525/173.
|
| 4343839 | Aug., 1982 | Blegan | 427/340.
|
| 4365039 | Dec., 1982 | Blegan | 524/773.
|
| 4374167 | Feb., 1983 | Blegan | 428/141.
|
| 4374181 | Feb., 1983 | Blegan | 428/423.
|
| 4877838 | Oct., 1989 | Toman | 525/107.
|
| 4888441 | Dec., 1989 | Calbo, Jr. et al. | 560/198.
|
| 4922002 | May., 1990 | Calbo, Jr. et al. | 528/286.
|
| 5166289 | Nov., 1992 | Yezrielev et al. | 525/443.
|
| 5210155 | May., 1993 | Yezrielev et al. | 525/442.
|
| 5235006 | Aug., 1993 | Jones et al. | 525/510.
|
| 5239018 | Aug., 1993 | Yezrielev et al. | 525/418.
|
| 5322884 | Jun., 1994 | Wellman et al. | 524/601.
|
| 5326831 | Jul., 1994 | Yezrielev et al. | 525/437.
|
| 5334652 | Aug., 1994 | Wellman et al. | 524/601.
|
| 5334671 | Aug., 1994 | Yezrielev et al. | 525/443.
|
| 5453469 | Sep., 1995 | Yezrielev et al. | 525/418.
|
| 5458920 | Oct., 1995 | Yezrielev et al. | 427/385.
|
| Foreign Patent Documents |
| 2809768 | Sep., 1978 | DE.
| |
| 05155840 | Jun., 1993 | JP.
| |
| 1290848 | Sep., 1972 | GB.
| |
Other References
Stumpe et al., "Deactivation of Excited States in Polyurethanes by Energy
Transfer to Salicyclic Acid Derivatives and its Application to the
Photo-stabilisation of Polyurethanes", Polymer Degradation and Stability
17 (1987) 103-115.
|
Primary Examiner: Clark; W. Robinson H.
Attorney, Agent or Firm: Jordan; Richard A., Hunt; John F.
Claims
What is claimed is:
1. A crosslinkable coating composition comprising a mixture of:
a. a poly(oligo)meric polymer component selected from the group consisting
of di(poly)esters, polyesters, alkyd resins, acrylic resins, polyether
polymers polycarbonate resins, and poly(oligo)mers which contain a
combination of two or more of ester, ether, carbonate, acrylic and alkyd
moieties in their structure, said polymeric component further
characterized as having a number average molecular weight within the range
of about 250 to about 20,000; and
b. a phenolic ester alcohol which has only one phenol group having at least
one reactive phenolic hydroxyl, wherein the phenolic ester alcohol also
has at least one aliphatic hydroxyl group and at least one ester group,
the phenolic hydroxyl and aliphatic hydroxyl being effective for reaction
with a crosslinker to cure the coating composition into a cured coating.
2. The composition of claim 1 which further contains: (c) a crosslinking
agent for said polymer component.
3. The composition of claim 2, wherein the phenolic ester alcohol is the
reaction product of a phenol carboxylic acid and an epoxy-functional
compound and said crosslinking agent is a methylol(alkoxymethyl)amino
crosslinking agent present in an amount effective to crosslink the
composition.
4. The composition of claim 1 wherein said phenolic ester alcohol has the
structure:
##STR14##
wherein R.sub.4 is selected from the group consisting of hydrogen,
halogen, hydroxyl, C.sub.1 to C.sub.8 alkyl and C.sub.1 to C.sub.8 alkoxy,
R.sub.5 is a direct bond or a C.sub.1 to C.sub.20 organic radical, R.sub.6
is hydrogen or a C.sub.1 to C.sub.20 organic radical which may form with
R.sub.7 part of a 5 or 6 carbon atom cyclic ring structure, R.sub.7 is
CH.sub.2 R.sub.8 wherein R.sub.8 is selected from the group consisting of
hydroxy, OR.sub.9, OOCR.sub.10 and R.sub.11 wherein R.sub.9 is a primary
or secondary aliphatic group containing 3 to 20 carbon atoms or an
aromatic group containing 6 to 20 carbon atoms, R.sub.10 is a primary,
secondary or tertiary aliphatic group containing 4 to 20 carbon atoms or
an aromatic group containing 6 to 20 carbon atoms, and R.sub.11 is a
C.sub.2 to C.sub.20 organic radical which may form with R.sub.6 part of a
5 or 6 carbon atom cyclic ring structure.
5. The composition of claim 4 wherein R.sub.4 and R.sub.6 are each
hydrogen, R.sub.5 is a direct bond and R.sub.7 is selected from the group
consisting of CH.sub.2 OH, a hydrocarbon moiety containing 3 to about 20
carbon atoms and an organic moiety containing ester or ether groups and
containing from 3 to about 20 carbon atoms.
6. The composition of claim 3 wherein said phenol carboxylic acid is a
hydroxybenzoic acid.
7. The composition of claim 3 wherein said epoxy functional compound is a
glycidyl ether or ester containing a terminal epoxy group.
8. The composition of claim 3 wherein said phenol carboxylic acid is
para-hydroxybenzoic acid.
9. The composition of claim 3 wherein said ester reaction product has a
molecular weight in the range of from about 250 to about 1000.
10. The composition of claim 3 wherein said ester reaction product is the
reaction product of para-hydroxybenzoic acid and a glycidyl ester of one
or a mixture of aliphatic acids containing 5 to 13 carbon atoms.
11. The composition of claim 10 wherein said reaction product is the
gylcidyl ester of an aliphatic acid containing an average of 9 to 11
carbon atoms.
12. The composition of claim 3 wherein said ester reaction product is
present in said composition at a level of from about 1 to about 60% by
weight based on the combined weight of said polymer and amino crosslinking
agent taken together.
13. The composition of claim 12 wherein said ester reaction product is
present at a level of from about 2 to about 30% by weight, based on the
combined weight of said polymer and amino crosslinking agent taken
together.
14. The composition of claim 3 wherein said polymeric component has a
number average molecular weight within the range of about 250 to about
10,000.
15. The composition of claim 14 wherein said molecular weight is in the
range of from about 250 to about 6,000.
16. The composition of claim 3 wherein said polymeric component is a
diester or polyester polymer having the structure:
##STR15##
wherein n is 0 or an integer ranging from 1 to about 40, R.sub.2 is a
divalent aliphatic or cycloaliphatic radical containing from 2 to about 40
carbon atoms or a mixture of such radicals, and R.sub.3 is a divalent
aliphatic, cycloaliphatic or aromatic radical containing from 2 to about
40 carbon atoms, or a mixture of such radicals.
17. The composition of claim 16 wherein n is 0.
18. The composition of claim 16 wherein n ranges from 1 to about 40.
19. The composition of claim 3 wherein said polymeric component is an alkyd
resin.
20. The composition of claim 3 wherein said polymeric component is a
polycarbonate polymer having the structure:
##STR16##
wherein q is an integer ranging from 1 to about 40, n is an integer
ranging from 0 to 40, R.sub.2 is a divalent aliphatic or cycloaliphatic
radical containing from 2 to about 40 carbon atoms or a mixture of such
radicals and R.sub.3 is a divalent aliphatic, cycloaliphatic or aromatic
radical containing from 2 to about 40 carbon atoms, or a mixture of such
radicals.
21. The composition of claim 17 wherein said polymeric component is the
diester condensation product of neopentyl glycol and adipic acid present
in a respective molar ratio of about 2 to 1.
22. The composition of claim 18 wherein said polymeric component is the
polyester condensation product of neopentyl glycol and adipic acid,
present at a respective molar ratio of p+1 to p wherein p is the number of
moles of adipic acid.
23. The composition of claim 3 wherein said methylol(alkoxymethyl)amino
crosslinking agent is present at a level of from about 3 to about 60
percent by weight, based on the combined weight of crosslinking agent and
crosslinkable polymer components.
24. The composition of claim 23 wherein said amino crosslinking agent is
hexamethoxymethyl melamine or hexaethoxymethyl melamine.
25. The composition of claim 3 further containing an organic solvent.
26. The composition of claim 3 further containing pigment.
27. A process for preparing a cured coating composition comprising:
a. applying the coating composition of claim 1 to a substrate;
b. drying said coating; and
c. heating said coated substrate for a time and a temperature sufficient to
cure said coating.
28. The process of claim 27 wherein said coating composition contains an
organic solvent.
29. A cured coating composition prepared by the process of claim 27.
30. A process for preparing a crosslinkable coating composition comprising
forming a mixture comprising:
a. a poly(oligo)meric polymer component selected from the group consisting
of di(poly)esters, polyesters, alkyd resins, acrylic resins, polyether
polymers, polycarbonate resins, and poly(oligo)mers which contain a
combination of two or more of ester, ether, carbonate, acrylic and alkyd
moieties in their structure, said polymeric component further
characterized as having a number average molecular weight within the range
of about 250 to about 20,000;
b. a phenolic ester alcohol which is an ester reaction product of a phenol
carboxylic acid and mono glycidyl compound; and
c. a crosslinking agent for said polymer component.
31. The process of claim 30 wherein said crosslinking agent is a
methylol(alkoxymethyl)amino crosslinking agent present in an amount
effective to crosslink the composition.
32. The process of claim 31 wherein said ester reaction product has the
structure:
##STR17##
wherein R.sub.4 is selected from the group consisting of hydrogen,
halogen, hydroxyl, C.sub.1 to C.sub.8 alkyl and C.sub.1 to C.sub.8 alkoxy,
R.sub.5 is a direct bond or a C.sub.1 to C.sub.20 organic radical, R.sub.6
is hydrogen or a C.sub.1 to C.sub.20 organic radical which may form with
R.sub.7 part of a 5 or 6 carbon atom cyclic ring structure, R.sub.7 is
CH.sub.2 R.sub.8 wherein R.sub.8 is selected from the group consisting of
hydroxy, OR.sub.9, OOCR.sub.10 and R.sub.11 wherein R.sub.9 is a primary
or secondary aliphatic group containing 3 to 20 carbon atoms or an
aromatic group containing 6 to 20 carbon atoms, R.sub.10 is a primary,
secondary or tertiary aliphatic group containing 4 to 20 carbon atoms or
an aromatic group containing 6 to 20 carbon atoms, and R.sub.11 is a
C.sub.2 to C.sub.20 organic radical which may form with R.sub.6 part of a
5 or 6 carbon atom cyclic ring structure.
33. The process of claim 32 wherein R.sub.4 and R.sub.6 are each hydrogen,
R.sub.5 is a direct bond and R.sub.7 is selected from the group consisting
of CH.sub.2 OH, a hydrocarbon moiety containing 3 to about 20 carbon atoms
and an organic moiety containing ester or ether groups and containing from
3 to about 20 carbon atoms.
34. The process of claim 33 wherein said phenol carboxylic acid is
para-hydroxybenzoic acid.
35. The process of claim 33 wherein said ester reaction product is the
reaction product of para-hydroxybenzoic acid and a glycidyl ester of one
or a mixture of aliphatic acids containing 5 to 13 carbon atoms.
36. A crosslinkable coating composition comprising a mixture of:
a. a poly(oligo)meric polymer component selected from the group consisting
of di(poly)esters, polyesters, alkyd resins, acrylic resins, polyether
polymers polycarbonate resins, and poly(oligo)mers which contain a
combination of two or more of ester, ether, carbonate, acrylic and alkyd
moieties in their structure, said polymeric component further
characterized as having a number average molecular weight within the range
of about 250 to about 20,000; and
b. a phenolic ester alcohol which is a reaction product of a phenol
carboxylic acid and a mono glycidyl compound selected from the group
consisting of a mono glycidyl ether and mono glycidyl ester.
37. The crosslinkable coating composition as recited in claim 36 wherein
the phenolic ester alcohol has a molecular weight in the range of from
about 250 to about 100.
38. The crosslinkable coating composition recited in claims 36 or 37
wherein the phenol carboxylic acid is hydroxybenzoic acid.
39. The crosslinkable coating composition recited in claim 38 wherein the
phenol carboxylic acid is para-hydroxybenzoic acid.
40. The crosslinkable coating composition recited in claims 36 or 37
wherein the mono glycidyl compound is a glycidyl ester having the formula
##STR18##
wherein R.sub.10 is a primary, secondary or tertiary aliphatic group
having 4 to 20 carbon atoms.
41. The crosslinkable coating composition recited in claim 38 wherein the
mono glycidyl compound is a glycidyl ester having the formula
##STR19##
wherein R.sub.10 is a primary, secondary or tertiary aliphatic group
having 4 to 20 carbon atoms.
42. A crosslinkable coating composition comprising a mixture of:
a. a polymer component having a number average molecular weight within the
range of about 250 to about 20,000 and having a hydroxyl functionality
which is effective for reaction with a crosslinker; and
b. a phenolic ester alcohol having the structure
##STR20##
wherein R.sub.4 is selected from the group consisting of hydrogen,
halogen, hydroxyl, C.sub.1 to C.sub.8 alkyl and C.sub.1 to C.sub.8 alkoxy,
R.sub.5 is a direct bond or a C.sub.1 to C.sub.20 organic radical, R.sub.6
is hydrogen or a C.sub.1 to C.sub.20 organic radical which may form with
R.sub.7 part of a 5 or 6 carbon atom cyclic ring structure, R.sub.7 is
CH.sub.2 R.sub.8 wherein R.sub.8 is selected from the group consisting of
hydroxy, OR.sub.9, OOCR.sub.10 and R.sub.11 wherein R.sub.9 is a primary
or secondary aliphatic group containing 3 to 20 carbon atoms or an
aromatic group containing 6 to 20 carbon atoms, R.sub.10 is a primary,
secondary or tertiary aliphatic group containing 4 to 20 carbon atoms or
an aromatic group containing 6 to 20 carbon atoms, and R.sub.11 is a
C.sub.2 to C.sub.20 organic radical which may form with R.sub.6 part of a
5 or 6 carbon atom cyclic ring structure.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to crosslinkable polymer compositions, to
solid crosslinked polymer compositions prepared therefrom, and to methods
for improving coating properties of films and surface coatings based
thereon.
2. Description of Related Art
Thermosettable coating formulations, particularly alkyd, acrylic, polyester
or diester-based coating compositions, are often the materials of choice
for application to various substrates, particularly metal substrates, as a
paint or a protective coating. Such coatings can be formulated to provide
a good balance of properties such as hardness, flexibility, solvent
resistance, corrosion resistance, weatherability and gloss. The
enhancement of these properties depends on many factors including type,
molecular weight, monomer composition, and glass transition temperature
(Tg) of the resin; type and amount of the crosslinker; curing conditions;
curing catalysts; pigments; fillers and additives. Variations of these
parameters can be used to create a wide range of differences in film
properties to fit requirements for a number of diverse applications.
However, it is not always possible to optimize all of the desirable
properties simultaneously.
The hardness of thermoset coating compositions can usually be increased by
either providing a resin monomer composition having high glass transition
temperature or by increasing the crosslink density.
The achievement of increased hardness by increasing polymer Tg gives rise
to polymers having increased viscosity which in turn may require the use
of larger than desirable quantities of solvent to form solutions suitable
for coating processes.
On the other hand, an increase in crosslink density of di- or
polyhydroxy-containing polymers containing a multifunctional crosslinking
agent such as a multi-alkoxy methyl amino crosslinking agent may be
achieved by increasing the concentration of the hydroxy functional groups
present in the polymer. For example, polyester polymers made by condensing
a dibasic acid and an excess of diol and containing terminal hydroxyl
groups and having a low molecular weight contain a greater number of
terminal hydroxy groups available as crosslinking sites than do the higher
molecular weight materials. Thus, an increase in hardness of such resins
can be achieved simultaneously with a reduction in viscosity and a
reduction of the volatile solvent content of coating and paint
formulations.
However, a very high degree of crosslinking tends to seriously reduce the
flexibility and may also affect other properties of the cured coating.
Also, the use of high levels of crosslinking agents needed for a high
degree of crosslinking results in the formation of a large amount of
volatile by-products of the crosslinking reaction which is undesirable in
such coating formulations.
One technique for improving the hardness and other properties of such
coatings is the inclusion in the curable composition of from about 1 to 60
wt % of a bis phenolic compound, e.g., bisphenol-A, as disclosed in U.S.
Pat. No. 5,166,289. The polyhydric phenol component participates in the
crosslinking reaction involving the base resin and the amino crosslinking
agent, thereby providing cured coatings of increased hardness.
However, the bisphenols tend to be poorly soluble in solvents normally used
in such compositions, and additional solvent quantities may be needed to
provide the requisite solubility. The inclusion of large amounts of
solvent to provide more workable viscosities also increases the content of
volatiles present in the composition, which is undesirable.
U.S. Pat. No. 4,331,782 discloses phenol-functional polyester resins which
are vapor-curable using isocyanate crosslinking agents. The
phenol-functional resins are prepared by first forming an ester-alcohol
adduct of a hydroxybenzoic acid and an epoxy compound, and then forming
the polyester by a polyesterification reaction including the adduct, a
polyol and a dibasic acid as reactants. The polyester resins are
characterized as being capped by the phenol-functional adduct.
SUMMARY OF THE INVENTION
The present invention provides for crosslinkable coating formulations based
on a mixture of a di or polyhydroxy functional poly(oligo)meric component
selected from the group consisting of di(poly)esters, polyesters, alkyd
polymers, acrylic polymers, polyethers, polycarbonate polymers and
poly(oligo)mers which contain a combination of two or more of ester,
ether, carbonate, acrylic and alkyd moieties in their structure; a
crosslinking agent and a reactive additive which is the ester reaction
product of a phenol carboxylic acid; and an epoxy compound. Preferred
ester reaction products have the general formula A:
##STR1##
wherein R.sub.4 is selected from the group consisting of hydrogen,
halogen, hydroxyl, C.sub.1 to C.sub.8 alkyl and C.sub.1 to C.sub.8 alkoxy,
R.sub.5 is a direct bond or a C.sub.1 to C.sub.20 organic radical which
may incorporate another phenol or aliphatic hydroxyl, ester, ether and/or
carbonate group in its structure, R.sub.6 is hydrogen or a C.sub.1 to
C.sub.20 organic radical or a direct bond which may form with R.sub.7 part
of a 5 or 6 carbon atom cyclic ring structure, R.sub.7 is CH.sub.2 R.sub.8
wherein R.sub.8 is selected from the group consisting of hydroxy,
OR.sub.9, OOCR.sub.10 and R.sub.11 wherein R.sub.9 is a primary or
secondary aliphatic group containing 3 to 20 carbon atoms or an aromatic
group containing 6 to 20 carbon atoms, R.sub.10 is a primary, secondary or
tertiary aliphatic group containing 4 to 20 carbon atoms or an aromatic
group containing 6 to 20 carbon atoms, and R.sub.11 is a C.sub.2 to
C.sub.20 organic radical which may form with R.sub.6 part of a 5 or 6
carbon atom cyclic ring structure.
More particularly, the present invention provides a crosslinkable coating
composition comprising a mixture of:
(a.) a di- or polyhydroxy functional oligomeric or polymeric component
selected from the group consisting of a polyester, a diester of a
di(poly)ol and a dicarboxylic acid, an alkyd resin, a polyether, an
acrylic resin and a polycarbonate resin, said polymeric component further
characterized as having a number average molecular weight within the range
of about 250 to about 20,000;
(b.) an ester reaction product of a phenol carboxylic acid and an epoxy
functional compound; and
(c.) a methylol(alkoxymethyl)amino crosslinking agent present in an amount
effective to crosslink the composition.
The crosslinkable compositions of this invention may be used to prepare
curable coating and paint formulations having workable (sprayable)
viscosities and reduced VOC content. The compositions may also contain
other ingredients such as a crosslinking catalyst, fillers, pigments and
the like. When cured, the coatings of this invention generally exhibit
improved hardness properties when compared with cured coatings which do
not contain the epoxy-ester reaction product additive. The presence of the
additive also serves to eliminate the problem of coating softening when
the coated substrate is baked for a prolonged period of time. These cured
coatings also have good weatherability, good corrosion resistance and
hydrolytic stability, enhanced oxidative and radiation stability, good
solvent and sag resistance and good adhesion properties.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on the fact that low molecular weight
reactive additives of the invention, when they are mixed with hydroxy
functional polymers and the preferred methylol (alkoxy methyl) amino
curing agents, form crosslinkable compositions in which both the hydroxy
functional polymers and the epoxy/phenol carboxylic acid reaction product
participate in the crosslinking reaction at baking conditions. As a
result, polymer structures, including highly crosslinked polymer
structures, can be built at baking conditions with the use of very low
molecular weight raw materials and low solvent quantities.
As indicated above, the oligomeric or polymeric component of the
composition of this invention may comprise a di- or polyhydroxy functional
polymer including a diester, a polyester, an alkyd polymer, an acrylic
polymer, a polyether, a polycarbonate polymer, or mixtures of two or more
of these materials.
Suitable diesters and polyesters are materials having the general formula
I:
##STR2##
wherein n is 0 or an integer ranging from 1 to about 40, R.sub.2 is a
divalent aliphatic or cycloaliphatic radical containing from 2 to about 40
carbon atoms or a mixture of such radicals, and R.sub.3 is a divalent
aliphatic, cycloaliphatic or aromatic radical containing from 2 to about
40 carbon atoms, or a mixture of such radicals. Obviously, when n is 0 in
formula I, a simple diester is represented. When n ranges from 1 to about
40, a polyester is represented.
In the more preferred embodiments of the invention, R.sub.2 is the divalent
residuum of a di(poly)ol containing from 2 to about 20 carbon atoms, more
preferably from about 2 to 10 carbon atoms, and may also contain internal
ester groups.
Some preferred examples of the diols are one or more of the following:
neopentyl glycol; ethylene glycol; hexamethylenediol;
1,2-cyclohexanedimethanol; 1,3-cyclohexanedimethanol;
1,4-cyclohexanedimethanol; diethylene glycol; triethylene glycol;
tetraethylene glycol; dipropylene glycol; polypropylene glycol; hexylene
glycol; 2-methyl-2-ethyl-1,3-propanediol; 2-ethyl-1,3-hexandediol;
1,5-pentanediol; thiodiglycol; 1,3-propanediol; 1,2-propanediol;
1,2-butanediol; 1,3-butanediol; 2,3-butanediol; 1,4-butanediol;
2,2,4-trimethyl-1,3-pentanediol; 1,2-cyclohexanediol; 1,3-cyclohexanediol;
1,4-cyclohexanediol; neopentyl diol hydroxy methyl isobutyrate, and
mixtures thereof. Examples of polyols include triols such as glycerine,
timethylol ethane, trimethylol propane, pentaerythritol and the like.
R.sub.3 in formula I above is the divalent residuum of a dicarboxylic acid
having from 2 to abut 40 aliphatic carbon atoms, from about 5 to 40
cycloaliphatic carbon atoms or from 6 to about 40 aromatic carbon atoms,
as well as mixtures of these acids. The carboxyl groups may be present in
the form of anhydride groups, lactone groups, or equivalent ester forming
derivatives such as the acid halide or methyl ester. The dicarboxylic
acids or derivatives are preferably one or more of the following: phthalic
anhydride, terephthalic acid, isophthalic acid, naphthalene dicarboxylic
acids, adipic acid, succinic acid, glutaric acid, fumaric acid, maleic
acid, cyclohexane dicarboxylic acid, azeleic acid, sebasic acid, dimer
acid, caprolactone, propiolactone, pyromellitic dianhydride, substituted
maleic and fumaric acids such as citraconic, chloromaleic, mesaconic, and
substituted succinic acids such as aconitic and itaconic, and mixtures
thereof. Many commercially available polyesters are produced using a
combination of aromatic and aliphatic dicarboxylic acids or a combination
of cycloaliphatic and aliphatic dicarboxylic acids or combinations of all
three types. However, where polyesters having low viscosity and low
solvent content are desired, the most preferred acids used for the
purposes of this invention are linear saturated or unsaturated aliphatic
dicarboxylic acids having from 2 to 10 carbon atoms such as succinic,
glutaric, adipic, and similar materials.
The acrylic polymers which may be used as a polymeric component in the
present invention are acrylic copolymer resins. The acrylic copolymer
resin is prepared from at least one hydroxy-substituted alkyl
(meth)acrylate and at least one non-hydroxy-substituted alkyl
(meth)acrylate. The hydroxy-substituted alkyl (meth)acrylates which can be
employed as monomers comprise members selected from the group consisting
of the following esters of acrylic or methacrylic acid and aliphatic
glycols: 2-hydroxyethyl acrylate, 3-chloro-2-hydroxypropyl acrylate;
1-hydroxy-2-acryloxy propane; 2-hydroxypropyl acrylate;
3-hydroxypropylacrylate; 2,3-dihydroxypropylacrylate; 3-hydroxybutyl
acrylate; 2-hydroxybutyl acrylate; 4-hydroxybutyl acrylate;
diethyleneglycol acrylate; 5-hydroxypentyl acrylate; 6-hydroxyhexyl
acrylate; triethyleneglycol acrylate; 7-hydroxyheptyl acrylate;
1-hydroxy-2-methacryloxy propane; 2-hydroxypropyl methacrylate;
2,3-dihydroxypropyl methacrylate; 2-hydroxybutyl methacrylate;
3-hydroxybutyl methacrylate; 2-hydroxyethyl methacrylate;
4-hydroxybutylmethacrylate; 3,4-dihydroxybutyl methacrylate;
5-hydroxypentyl methacrylate; and 7-hydroxyheptyl methacrylate. The
preferred hydroxy functional monomers for use in preparing the acrylic
resins are hydroxy-substituted alkyl (meth)acrylates having a total of 5
to 7 carbon atoms, i.e., esters of C.sub.2 to C.sub.3 dihydric alcohols
and acrylic or methacrylic acids. Illustrative of particularly suitable
hydroxy-substituted alkyl (meth)acrylate monomers are 2-hydroxyethyl
methacrylate, 2-hydroxyethyl acrylate, 2-hydroxybutyl acrylate,
2-hydroxypropyl methacrylate, and 2-hydroxypropyl acrylate.
Among the non-hydroxy-substituted alkyl (meth)acrylate monomers which may
be employed are alkyl (meth)acrylates. Preferred nonhydroxy unsaturated
monomers are esters of C.sub.1 to C.sub.12 monohydric alcohols and acrylic
or methacrylic acids, e.g., methyl methacrylate, hexyl acrylate,
2-ethylhexyl acrylate, lauryl methacrylate, glycidyl methacrylate, etc.
Examples of particularly suitable monomers are butyl acrylate, butyl
methacrylate and methyl methacrylate.
Additionally, the acrylic copolymer resins used in the present invention
may include in their composition other monomers such as acrylic acid and
methacrylic acid, monovinyl aromatic hydrocarbons containing from 8 to 12
carbon atoms (including styrene, alpha-methyl styrene, vinyl toluene,
t-butyl styrene, chlorostyrene and the like), vinyl chloride, vinylidene
chloride, acrylonitrile, epoxy-modified acrylics and methacrylonitrile.
The acrylic copolymer preferably has a number average molecular weight not
greater than 20,000, more preferably between about 500 and 6000, and most
preferably between about 1000 and 5000.
Alkyd polymers which may be used as the polymeric component of the
composition of this invention have a formula similar to formula I above
except that R.sub.2 is a divalent residuum of a triol with one hydroxyl
group esterified with a fatty acid. Typical triols are glycerine,
trimethylol ethane and like materials. These alkyd resins are oil modified
polyester resins and are broadly the product of the reaction of a dihydric
alcohol and a dicarboxylic acid or acid derivative and an oil, fat or
carboxylic acid derived from such oil or fat which acts as a modifier.
Such modifiers are typically drying oils. The polyhydric alcohol employed
is suitably an aliphatic alcohol, and mixtures of the alcohols may also be
employed. The dicarboxylic acid, or corresponding anhydrides, may be
selected from a variety of aliphatic carboxylic acids or mixtures of
aliphatic and aromatic dicarboxylic acids. Suitable acids and acid
anhydrides include, by way of example, succinic acid, adipic acid,
phthalic anhydride, isophthalic acid, trimellitic acid (anhydride) and bis
3,3',4,4'-benzophenone tetracarboxylic anhydride. Mixtures of these acids
and anhydrides may be employed to produce a balance of properties. As the
drying oil or fatty acid there is suitably employed a saturated or
unsaturated fatty acid of 12 to 22 carbon atoms or a corresponding
triglyceride, that is, a corresponding fat or oil, such as those contained
in animal or vegetable fats or oils. Suitable fats and oils include tall
oil, castor oil, coconut oil, lard, linseed oil, palm oil, peanut oil,
rapeseed oil, soybean oil and beef tallow. Such fats and oils comprise
mixed triglycerides of such fatty acids as caprylic, capric, lauric,
myristic, palmitic, and stearic and such unsaturated fatty acids as oleic,
eracic, ricinoleic, linoleic and linolenic. Chemically, these fats and
oils are usually mixtures of two or more members of the class. Alkyd
resins made with saturated monocarboxylic acids and fats are preferable
where improved weather resistance is of prime concern.
Polycarbonate oligomers or polymers which may be used in preparing the
compositions of this invention are hydroxy terminated polycarbonates
having the general formula II:
##STR3##
wherein q is an integer ranging from 1 to about 40, n is an integer
ranging from 0 to 40, and R.sub.2 and R.sub.3 are as defined above. This
formula includes diesters wherein n is 0 and q is 1 or greater which may
be prepared by forming the condensation product of an aliphatic or
cycloaliphatic diol having 2 to about 40 carbon atoms with a carbonic acid
bis-aryl ester, such as diphenyl carbonate, followed by subsequent
polycondensation reaction of this intermediate with said diol.
Also included in formula II are polyester diols lengthened via carbonate
linkages and containing terminal carbonate groups linking the lengthened
polyester diol backbone to terminal hydroxy-containing end groups, in
which case n in formula II is equal to or greater than 1 and q is greater
than 1.
A third category of polycarbonate within the scope of formula II are
polyester diols containing terminal carbonate groups linking the polyester
diol backbone to hydroxy-containing end groups, in which case q in formula
II is equal to 1 and n is greater than 1. These materials may be prepared
by forming the condensation product of a polyester diol with a carbonic
acid bis-aryl ester, such as diphenyl carbonate, to form the
polyester-diol bis-carbonic acid ester, followed by polycondensation of
this precursor with a diol to form hydroxy terminated diesters.
The polymeric component may also comprise poly(oligo)mers which contain a
combiantion of two or more of ester, ether, carbonate, acrylic and alkyd
moieties in their structure. Examples of such materials are
poly(ether)esters, poly(ether) carbonates and poly(ether) or poly(ester)
acrylics.
The diesters and polyesters may be prepared by well known condensation
processes using a molar excess of diol. Preferably the molar ratio of diol
to dicarboxylic acid is p+1:p wherein p represents the number of moles of
dicarboxylic acid. The reaction may be conducted in the absence of or
presence of an aromatic or aliphatic solvent and in the absence of or
presence of a suitable polycondensation catalyst as is known in the art.
The preferred number average molecular weight (Mn) of the polymers may
generally range from about 250 up to about 20,000, more preferably from
about 280 up to about 10,000, and most preferably from about 300 up to
about 3,000 to 6,000. Glass transition temperatures (Tg) of these
materials may generally range from as low as -40.degree. C. up to
+100.degree. C. or higher.
The reactive additives used in the curable compositions of this invention
are materials within the general structure of formula A above. The phenol
carboxylic acid reactant used to prepare the ester reaction product of
formula A has the general structure:
##STR4##
wherein R.sub.4 and R.sub.5 are as described above. Examples of suitable
phenol carboxylic acids include hydroxybenzoic acids, acids where R.sub.5
is alkylene such as phenyl acetic acid, hydroxy phenyl propionic acid,
hydroxyphenyl stearic acid, and acids wherein R.sub.5 encompasses
additional phenol functionality such as 4,4-bis hydroxyphenyl pentanoic
acid and the like. In a preferred embodiment of the invention, R.sub.4 in
formula A is hydrogen, R.sub.5 is a direct bond, R.sub.6 is hydrogen and
R.sub.7 is CH.sub.2 OH, a hydrocarbon moiety or an organic moiety
containing ester or ether groups and containing from 1 to about 20 carbon
atoms, more preferably from about 3 to 20 carbon atoms.
A particular advantage with the use of the reactive additives of this
invention as compared, for example, with the bisphenol-A type materials
disclosed in U.S. Pat. No. 5,166,289 is that the present materials are
generally more soluble in the solvents conventionally used in paint
formulations and are in many cases more compatible with other ingredients
present in the formulation. Thus, formulations of low viscosity which are
either solvent free or contain lesser amounts of solvent can be prepared,
thereby lowering the content of volatile organic compounds (VOC) present
in the formulation.
The preferred reactive additives used in the curable compositions of this
invention are the ester reaction products of a hydroxybenzoic acid and an
epoxy compound. Suitable hydroxybenzoic acids include ortho-hydroxybenzoic
acid (salicylic acid), meta-hydroxybenzoic acid and para-hydroxybenzoic
acid (PHBA), with para-hydroxybenzoic acid being most preferred.
The epoxy compound may be selected from the group consisting of glycidyl
esters, glycidyl alcohols, glycidyl ethers, linear epoxies and aromatic
epoxies. These include glycidol, glycidyl ethers of the structure:
##STR5##
glycidyl esters of the structure:
##STR6##
glycidyl or oxirane compounds having the structure:
##STR7##
and cycloaliphatic epoxy compounds having the structures:
##STR8##
wherein R.sub.12 is an organic radical having 1-12 carbon atoms which can
include ether, ester, hydroxyl or epoxy groups, as well as other
cycloiphatic compounds having the structures:
##STR9##
Other epoxy materials include epoxidized alpha-olefins and bis aromatic
epoxies such as the reaction product of bisphenol A or F with
epichlorohydrin.
Suitable epoxy compounds particularly include monoepoxides containing a
terminal glycidyl group or polyepoxides containing internal oxirane or
glycidyl groups or terminal glycidyl groups. Suitable epoxy compounds
include glycidol, glycidyl acrylate or methacrylate monomers, alkyl
glycidyl ether monomers, and low molecular weight copolymers of one or
more of these monomers with one or more ethylenically unsaturated monomers
such as acrylates, methacrylates, vinyl aromatic monomers and the like.
Other suitable epoxy compounds include the ester reaction products of
epichlorohydrin with mono- or dibasic aliphatic or aromatic carboxylic
acids or anhydrides containing from about 1-20 carbon atoms. Inclusive of
such acids are aliphatic acids such as acetic, butyric, isobutyric,
lauric, stearic, maleic and myristic acids and aromatic acids such as
benzoic, phthalic, isophthalic and terephthalic acids as well as the
corresponding anhydrides of such acids. Preferred such acids are primary,
secondary or tertiary aliphatic carboxylic acids containing from 5 to 13
carbon atoms. A preferred epoxy compound of this type is the glycidyl
ester of a mixed aliphatic, mostly tertiary, mono carboxylic acid with an
average of 9 to 11 carbon atoms such as available from Exxon Chemical Co.,
under the trade name GLYDEXX.RTM. or from Shell Chemical Co. under the
trade name CARDURA.RTM. E ester.
Still other epoxy compounds include glycidyl ether reaction products of
epihalohydrin with aliphatic or aromatic alcohols or polyols containing
from about 1 to 20 carbon atoms. Suitable alcohols include aromatic
alcohols such as benzyl alcohol; aromatic polyols such as bisphenol,
bisphenol A, bisphenol F, phenolphthalein and novolac resins; aliphatic
alcohols such as ethanol, isopropanol, isobutyl alcohol, hexanol, stearyl
alcohol and the like; and aliphatic polyols such as ethylene glycol,
propylene glycol and butylene glycol.
Other epoxy compounds which may be used include the mono-epoxides of
C.sub.8 to C.sub.20 alpha mono-olefins.
The epoxy compound may also comprise epoxidized fatty compounds. Such
epoxidized fatty compounds include epoxidized fatty oils, epoxidized fatty
acid esters of monohydric alcohols, epoxidized fatty acid esters of
polyhydric alcohols, epoxidized fatty nitriles, epoxidized fatty amides,
epoxidized fatty amines and epoxidized fatty alcohols. Suitable alicyclic
epoxide and polyepoxide materials include dicyclopentadiene diepoxide,
limonene diepoxide, and the like. Additional useful epoxides include for
example, vinyl cyclohexane dioxide, bis(3,4-epoxycyclohexyl)adipate,
3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexane carboxylate and
2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-metadioxane.
The preferred hydroxybenzoic acid/epoxy reaction product of this invention
may be formed by reacting the hydroxybenzoic acid and the epoxy compound,
optionally in a solvent therefor, at a temperature ranging from about
90.degree. to about 120.degree. C. to initiate such reaction. Once the
reaction is initiated, such reaction is exothermic, and the reaction
temperature can rise to a temperature of about 150.degree. to 175.degree.
C. usually without application of external heat. The reaction temperature
then is maintained at about 150.degree. to 170.degree. C. (and preferably
less than about 200.degree. C.) until the reaction has been determined to
be substantially complete.
Reaction products of reduced discoloration can be produced by control of
the maximum temperature of the exothermic reaction. This can be achieved
by a staged and/or incremental addition of one of the reactants, e.g. the
epoxy reactant, so that the reaction temperature is maintained at a
temperature of about 150.degree. C. or below. The remainder of that
reactant may then be added in stages or continuously while maintaining the
reaction temperature below about 150.degree. C. This process modification
gives rise to reaction products having lower Color Index values.
Approximately stoichiometric quantities of the epoxy compound and the
phenol carboxylic acid are used in the reaction, although a slight molar
excess of epoxy may be necessary to drive the reaction to completion.
The phenol carboxylic acid/epoxy reaction product may be blended with the
base polymer at a blend ratio of from 1 to about 60% by weight of reaction
product, based on the weight of base polymer and the crosslinking agent
taken together. More preferred compositions contain the reaction product
at a level of from about 2 to about 40% by weight, and most preferably at
a level of from about 3 to 20% by weight, based on the weight of the base
polymer and crosslinking agent taken together.
The preferred methylol(alkoxymethyl)amino crosslinking agents used in the
present invention are well known commercial products, and are generally
made by the reaction of di(poly)amide(amine) compounds with formaldehyde
and, optionally, a lower alcohol.
Examples of suitable amino-crosslinking resins include one or a mixture of
the following materials:
Melamine based resins
##STR10##
wherein R is the following: R=CH.sub.3 (Cymel.RTM. 300, 301, 303);
R=CH.sub.3, C.sub.2 H.sub.5 (Cymel.RTM. 1116);
R=CH.sub.3, C.sub.4 H.sub.9 (Cymel.RTM. 1130, 1133);
R=C.sub.4 H.sub.9 (Cymel.RTM. 1156); or
R=CH.sub.3 H (Cymel.RTM. 370, 373, 380, 385)
The preferred melamine is hexamethoxymethyl melamine.
Benzoguanamine based resins
##STR11##
wherein R=CH.sub.3, C.sub.2 H.sub.5 (Cymel.RTM. 1123)
Urea based resins
##STR12##
wherein R=CH.sub.3, H (Beetle.TM. 60, Beetle.TM. 65); or
R=C.sub.4 H.sub.9 (Beetle.TM. 80).
Gycoluryl based resins
##STR13##
wherein: R=CH.sub.3, C.sub.2 H.sub.5 (Cymel.RTM. 1171); or
R=C.sub.4 H.sub.9 (Cymel.RTM. 1170).
In the present invention, the ratio of the active crosslinking groups,
e.g., methylol(alkoxymethyl) groups of the amino crosslinking agent to the
terminal hydroxy groups on the curable components is desirably from about
1.0:1.0 to 15.0:1.0, more preferably from about 1.5:1.0 to 5.0:1.0, most
preferably from about 1.5:1.0 to 4.0:1.0.
On a weight basis, the amount of amino crosslinking agent effective for
curing the crosslinkable binder generally ranges from about 3 to about 60
percent by weight, more preferably from about 10 to about 50 percent by
weight based on the combined weight of the amino crosslinking agent,
polymer and any other crosslinkable polymer constituent of the
composition. In general, quantities of crosslinking agent required to cure
the composition are inversely proportional to the number average molecular
weight of the base polymer. Quantities of crosslinking agent on the higher
side of this range are required to properly cure polymer compositions
having a relatively low number average molecular weight, e.g., from about
250 to about 3,000, whereas lesser amounts of the crosslinking agent are
required to properly cure polymers having a higher number average
molecular weight, e.g., from about 3,000 up to about 20,000.
The composition of the invention may also be cured using one or more
multi-isocyanate crosslinking agents. Examples of such materials include
aromatic and aliphatic di- or polyisocyantes of the type disclosed in U.S.
Pat. No. 4,331,782, the complete disclosure of which is incorporated
herein by reference.
The quantity of crosslinking agent required to cure the base polymer
depends upon equivalent weight per hydroxyl of the base polymer. For
bis-hydroxyl functional polymers (polyesters), the equivalent weight is
equal to one-half the molecular weight. For polyfunctional polymers
(acrylics), the independent weight is essentially independent of molecular
weight and depends on the concentration of hydroxyl functional monomer in
the polymer or copolymer structure.
In general, the crosslinking agent and the ester reaction product of
formula A above are present in the composition at a respective weight
ratio of from about 40 to 75 parts by weight of crosslinking agent per 60
to 25 parts by weight of ester reaction product, more preferably from 50
to 70 parts by weight of the former per 50 to 30 parts by weight of the
latter.
The present invention also provides for a novel coating composition formed
by combining the oligomeric or polymer component, the phenol carboxylic
acid/epoxy reaction product component, the crosslinking agent, and
optionally a solvent. Application of the formulated coating can be made
via conventional methods such as spraying, roller coating, dip coating,
etc., and then the coated system may be cured by baking.
Suitable optional solvents which may be included in the curable
compositions of the invention comprise toluene, xylene, ethylbenzene,
tetralin, naphthalene, and solvents which are narrow cut aromatic solvents
comprising C.sub.8 to C.sub.13 aromatics such as those marketed by Exxon
Chemical Company under the name Aromatic 100, Aromatic 150, and Aromatic
200.
Other suitable solvents include acetone, methyl ethyl ketone, methyl
isobutyl ketone, methyl amyl ketone, methyl isoamyl ketone, methyl heptyl
ketone, isophorone, isopropanol, n-butanol, sec.-butanol, isobutanol, amyl
alcohol, isoamyl alcohol, hexanols, and heptanols.
Suitable oxygenated solvents include propylene glycol monomethyl ether
acetate, propylene glycol propyl ether acetate, ethyl ethoxypropionate,
dipropylene glycol monomethyl ether acetate, propylene glycol monomethyl
ether, and like materials. Other such solvents include alkyl esters such
as ethyl acetate, n-propyl acetate, butyl acetate, amyl acetate, mixtures
of hexyl acetates such as sold by Exxon Chemical Company under the name
EXXATE.RTM. 600 and mixtures of heptyl acetates sold under the name
EXXATE.RTM. 700. The list should not be considered as limiting, but rather
as examples of solvents which are useful in the present invention. The
type and concentration of solvents are generally selected to obtain
formulation viscosities and evaporation rates suitable for the application
and baking of the coatings. Typical solvent concentrations in the
formulations range from 0 to about 75% by weight with a preferred range
between about 5 and 50% by weight and a most preferred range between about
10 and 40% by weight. For the preparation of high solids coatings, the
amount of solvent used in the coating formulation is preferably less than
40% of the weight of the formulation.
Pigments are a further component which may be present in the curable
compositions of this invention. They are generally included at a weight
ratio in the range of from about 0.5 to about 5.0 to one pigment-to-binder
ratio, the term binder referring to the total weight of polymer plus
crosslinking agent.
Suitable pigments which may be included in the compositions of this
invention are those opacifying pigments normally used in paint and coating
formulations and include titanium dioxide, zirconium oxide, zircon, zinc
oxide, iron oxides, antimony oxide, carbon black, as well as chrome
yellows, greens, oranges, mixed metal oxides, ceramic pigments and the
like. Preferred pigments include rutile TiO.sub.2 and particularly weather
resistant coated types of TiO.sub.2. The pigments may also be blended with
a suitable extender material which does not contribute significantly to
hiding power. Suitable extenders include silica, barytes, calcium sulfate,
magnesium silicate (talc), aluminum oxide, aluminum hydroxide, aluminum
silicate, calcium silicate, calcium carbonate (mica), potassium aluminum
silicate and other clays or clay-like materials.
Satisfactory baking schedules for formulations of the present invention
vary widely including, but not limited to, low temperature bakes of about
20 to 30 minutes at temperatures between 90.degree. and 105.degree. C. for
large equipment applications and high temperature bakes of about 5 to 10
seconds in 300.degree. to 375.degree. C. air for coil coating
applications. In general, the substrate and coating should be baked at a
sufficiently high temperature for a sufficiently long time so that
essentially all solvents are evaporated from the film and chemical
reactions between the polymer and the crosslinking agent proceed to the
desired degree of completion. The desired degree of completion also varies
widely and depends on the particular combination of cured film properties
required for a given application.
Acid catalysts may be used to cure systems containing hexamethoxymethyl
melamine and other amino crosslinking agents, and a variety of suitable
acid catalysts are known to one skilled in the art for this purpose. These
include, for example, p-toluene sulfonic acid, methane sulfonic acid,
nonylbenzene sulfonic acid, dinonylnapthalene disulfonic acid,
dodecylbenzene sulfonic acid, phosphoric acid, phosphorous acid, phenyl
acid phosphate, butyl phosphate, butyl maleate, and the like or a
compatible mixture of them. These acid catalysts may be used in their
neat, unblocked form or combined with suitable blocking agents such as
amines. Typical examples of unblocked catalysts are the King Industries,
Inc. products with the tradename K-CURE.RTM.. Examples of blocked
catalysts are the King Industries, Inc. products with the tradename
NACURE.RTM..
The amount of catalyst employed typically varies inversely with the
severity of the baking schedule. In particular, smaller concentrations of
catalysts are usually required for higher baking temperatures or longer
baking times. Typical catalyst concentrations for moderate baking
conditions (15 to 30 minutes at 150.degree. C.) would be about 0.2 to 0.5
wt % catalyst solids per polymer plus crosslinking agent solids. Higher
concentrations of catalyst up to about 2 wt % may be employed for cures at
lower temperature or shorter times. Formulations containing sufficient
residual esterification catalyst, such as phosphorous acid, may not
require the inclusion of any additional crosslinking catalyst to effect a
proper cure at lower curing temperatures.
In the case of formulations of this invention containing hexamethoxymethyl
melamine as the crosslinking agent and p-toluene sulfonic acid as the
catalyst, preferred curing conditions at dry film thickness of about 1 mil
are catalyst concentration between about 0.05 and 0.6 wt %, based on
polymer solids plus crosslinking agent solids, baking temperature between
90.degree. and 210.degree. C. and baking time between about 5 and 60
minutes. Most preferred curing conditions are catalyst concentration
between about 0.05 and 0.5 wt. %, baking temperature between about
120.degree. and 180.degree. C. and baking time between about 5 and 40
minutes.
As described above, the formulations of this invention are characterized by
improved weather resistance. However, additional improvements in this and
other properties can be achieved by including stabilizers and stabilizing
systems into the formulation. Among compounds providing improvements in
weather resistance are HALS (hindered amine light stabilizers),
UV-screeners, and other antioxidants. Flow modifiers, rheology modifiers,
pigment dispersants and the like may also be included in the composition.
Coating formulations of the present invention may be prepared by first
forming a mill base. The mill base may be prepared by grinding a mixture
of pigment, resin and solvent in a high speed disc disperser such as
Byk-Gardner DISPERMAT.RTM. Model CV to form a pigment concentrate. This
mill base is then let down (mixed) under mixing conditions with the
remaining components of the formulation which include additional resin,
solvent, crosslinking agent, and the catalyst.
The coating compositions of the invention may be applied to substrates by
any suitable conventional technique such as spraying, roller coating, dip
coating and the like. The composition may be applied in liquid form, and
preferably is dispersed in an organic solvent. Typical solvent
concentrations in the formulations generally range from 0 to about 75% by
weight, with a preferred range of between about 5 and 50% by weight and a
most preferred range of between about 10 and 40% by weight.
The crosslink density and degree of crosslinking of the composition can be
monitored by evaluating the impermeability of the cured coating to organic
solvent. A suitable test for evaluating this property is MEK rub test as
described in paragraph 5.2 of ASTM D3732. This test measures the number of
double rubs of a swab soaked with methyl ethyl ketone (MEK) required to
completely remove the cured coating from a substrate. Generally speaking,
the coatings of this invention are crosslinked sufficiently such that MEK
rub values of greater than about 5, more preferably of at least 15 and
most preferably more than 50 or 100 are achieved.
Properly formulated binder paints and coatings comprising compounds of
structure A above provide at least one of the improvements listed below:
improved hardness-flexiblity balance
lower VOC at a workable viscosity
improved adhesion
improved anti-corrosive properties
improved solvent resistance
improved oxidative and/or radiation resistance
improved electric resistance
improved weather resistance
The following examples illustrate the preparation of some preferred
hardening agents and their use as a blend component in forming the curable
polymer compositions of the invention. Materials identified in the
examples by trade names are as follows:
GLYDEXX.TM.N-10--glycidal ester of a mixture of tertiary aliphatic acids
having 9-11 carbon atoms available from Exxon Chemical Co.
GLYDEXX.TM. ND-101--Same as N-10, but less pure.
ARALDITE.TM.DY-025--A C.sub.8 glycidyl ether available from Ciba Geigy
Corp.
CYRACURE.TM. 6216--A C.sub.16 linear epoxy available from Union Carbide.
CARGILL.TM.57-5789--A hydroxy functional polyester having a molecular
weight of 900-1,000 available from McWhorter Corp.
CARGILL.TM.57-5742--A short oil tofa-based alkyd resin also available from
McWhorter Corp.
RUCOFLEX.TM.S107-210--Neopentyl glycol adipate diester oligomer having a
molecular weight of about 560.
MIAK--Methyl isoamyl ketone
SOLVENT MIX--A mixture of methyl ethyl ketone, butyl acetate, xylene,
butanol and EXXATE.RTM.600 present at a respective weight ratio of
2:3:3:1:1.
HMMM--Hexamethoxymethyl melamine crosslinking agent.
BYK.TM.300--Silicone flow control agent from Byk-Chemie.
DC-57--Silicone flow control agent from Dow Corning.
BYK.TM. 451--Amine blocked p-toluene sulfonic acid catalyst from
Byk-Chemie.
NACURE.TM.2500--Blocked p-toluene sulfonic acid catalyst from King
Industries.
Examples 1-4 below illustrate the preparation of four different ester
reaction products of PHBA and various epoxy compounds, and the properties
of each.
EXAMPLE I
Synthesis of Glycidyl Ester+PHBA
Into a 1 liter flask equipped with agitation, nitrogen, heating and
temperature probe, 326.6 g Glydexx.RTM. N-10 glycidyl ester and 173.4 g
parahydroxy benzoic (PHBA) were charged. The mixture was heated at
110.degree. C. At that point, an exothermic reaction takes place. The
maximum temperature reached was 160.degree. C. At this point, the solution
was clear. The solution was then cooled and discharged. Physical
properties are given below.
______________________________________
Acid Number 0 mg KOH/gram
Hydroxyl Number 301.0 mg KOH/gram
NVM >99%
Color <3 Gardner
______________________________________
EXAMPLE 2
Synthesis of Glycidyl Ester & PHBA
Into a 3 liter flask equipped with heating agitation and nitrogen 326.6 g
Glydexx.RTM. ND-101 and 173.4 g parahydroxybenzoic acid (PHBA) were
charged. The mixture was heated to 110.degree. C. with agitation. At
approximately 110.degree. C. an exothermic reaction occured. The mixture
turned from a cloudy solution to a clear solution as the temperature
approached a maximum of 158.degree. C. The solution was cooled back to
room temperature. Physical characteristics are given below.
______________________________________
Acid Number 2.5 mg KOH/gram
Hydroxyl Value 417-mg KOH/gram
NVM 98.8 Wt. %
Color <3 Gardner
______________________________________
EXAMPLE 3
Synthesis of Glycidyl Ether+PHBA
200 g Araldite.RTM. DY025 and 87.6 g PHBA were charged into a 1 liter flask
equipped with agitation, heating and nitrogen. The mixture was heated to
135.degree. C. At 135.degree. C. an exothermic reaction occured. The
maximum temperature reached was 172.degree. C. At about 158.degree. C.,
the solution turned from cloudy to clear. The reaction was then cooled
back to room temperature. Physical characteristics are given below.
______________________________________
TAN 9.8 mg KOH/gram
Hydroxyl Number 360.0 mg KOH/gram
NVM 96.01 wt %
______________________________________
EXAMPLE 4
Synthesis of Linear Epoxy+PHBA
250 g Cyracure.RTM. 6216 and 124.2 g parahydroxy-benzoic acid were charged
into a 1 liter flask equipped with agitation, heating and nitrogen. The
reaction was heated to 150.degree. C. At that temperature an exothermic
reaction occurred and the temperature increased to 159.degree. C. The
temperature was held at 160.degree. C. The solution turned clear. To drive
the reaction to completion, the solution was maintained at 170.degree. C.
for four hours. The solution was then cooled to room temperature. Physical
properties are given below.
______________________________________
TAN 10.5 mg KOH/gram
Hydroxyl Number 294.0 mg KOH/gram
NVM 97.4%
______________________________________
Paint formulations having compositions as set forth in the following
examples were prepared by forming a mill base composition and a let down
composition by the general procedure described above.
Test panels were prepared and evaluated as follows:
Thin films of the various formulations were applied to steel test panels
via drawdowns. The basic procedures are outlined in ASTM Test Procedure
D823-87. Test panels are either untreated Type S cold rolled steel panels
obtained from the Q-Panel Company or polished Bonderite.TM. 1000
(iron-phosphate treatment) panels obtained from Advanced Coatings
Technology Inc. Panels sizes are either 4".times.8" or 3".times.6".
Wire-wound drawdown rods and in some cases a Precision Laboratory Drawdown
Machine (both from the Paul N. Garnder Company) are used to apply films
via hand-pulled drawdowns (Method E). Target dry film thicknesses are 1
mil.
The film property evaluations conducted on all cured panels were as
follows:
Knoop Hardness--ASTM D-1474
Direct Impact--ASTM D-2794
Reverse Impact--ASTM D-2794
VOC--EPA Method 24
Pencil Hardness--ASTM D-3363
Flexibility (T-bend)--ASTM D-1737
Adhesion--ASTM D-3359
Corrosion Resistance (Salt Spray)--ASTM B-117
MEK Rubs--ASTM D-3732
Weathering (QUV)--ASTM G-53
Sag Resistance--ASTM D-4400
In the case of the impact tests, a 5/8 inch punch with a 0.64 inch die was
employed.
EXAMPLE 5 (Control)
A polyester paint was formulated as follows:
______________________________________
Amount (g)
______________________________________
Millbase
Polyester (Cargill 57-5789)
15.8
TiO.sub.2 32.6
MIAK 1.6
Let Down
Polyester (Cargill 57-5789)
21.7
HMMM 9.0
BYR 451 0.8
BYK 300 0.1
MIAK 15.0
______________________________________
The resulting paint had a measured volatile organic compound (VOC) content
of 3.2 lb/gal. at a viscosity 29.8 seconds (Zahn Cup #2).
The paint was baked at 177.degree. C. for 10 minutes. One mil dry film
thickness paints were drawn on Bonderite 1000 panels. The results are
given below.
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 2H
Knoop Hardness 17.7
Direct Impact (lb-in)
160
T-bend (no pick) 2 T
Adhesion 5
Corrosion Resistance, Blistering
6
(Salt spray, 144 hrs.)
MEK Double Rubs 200
Gloss 60.degree. 97
Sag Resistance (mils)
1.3
______________________________________
EXAMPLE 6
The formulated paint of Example 5 was modified by adding the reaction
product of para-hydroxy benzoic acid (PHBA) and Glydexx.RTM. N-10 glycidyl
ester made as described in Example 1.
______________________________________
Amount (g)
______________________________________
Millbase
Polyester (Cargill 57-5789)
15.8
TiO.sub.2 32.6
MIAK 1.6
Let Down
Polyester (Cargill 57-5789)
14.2
HMMM 11.3
Ex. 1 reaction product
4.1
BYK 451 0.8
BYK 300 0.1
MIAK 14.2
______________________________________
The paint which had a measured VOC content of 3.0 lb/gal. at a viscosity of
28.4 seconds (Zahn #2), was baked at 177.degree. C. for 10 minutes. One
mil dry film thickness paints were drawn on Bonderite 1000 panels. Test
results are given below.
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 2H
Knoop Hardness 19.6
Direct Impact (lb-in)
160
T-bend (no pick) 2 T
Adhesion 5
Corrosion Resistance, Blistering
10
(Salt Spray, 144 hrs.)
MEK Double Rubs 200
Gloss 60.degree. 98
Sag Resistance (mils)
>1.4
______________________________________
EXAMPLE 7 (Control)
The following paint was made using a short oil Tofa alkyd.
______________________________________
Amount (g)
______________________________________
Millbase
Alkyd (Cargill 57-5742)
15.0
TiO.sub.2 34.1
MIAK 1.8
Let Down
Alkyd (Cargill 57-5742)
20.6
HMMM 10.7
BYK 451 0.8
BYK 300 0.1
MIAK 16.9
______________________________________
The resulting paint had a measured VOC content of 3.1 lb/gal. at a
viscosity of 25.0 seconds (Zahn #2). Panels were made by drawing down the
paint on Bonderite 1000 panels. The panels were cured at 177.degree. F.
for 10 minutes. The physical properties of the paint are given below.
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 2H
Knoop Hardness 16.5
Direct Impact (lb-in)
70
T-bend (no pick) 4 T
Adhesion 5
MEK Double Rubs 200
Gloss 60.degree. 99
______________________________________
EXAMPLE 8
The alkyd formulation of control Example 7 was modified by including the
reaction product prepared in Example 1 in the formulation.
______________________________________
Amount (g)
______________________________________
Millbase
Alkyd (Cargill 57-5742)
15.0
TiO.sub.2 34.1
MIAK 1.8
Let Down
Alkyd (Cargill 57-5742)
13.5
HMMM 12.7
Ex. 1 Reaction Product
4.2
BYK 451 0.8
BYK 300 0.1
MIAK 15.8
______________________________________
The resulting paint had a measured VOC content of 2.9 lb/gal. at a
viscosity of 25.7 seconds (Zahn #2). Painted panels were made by drawing
down the paint onto Bonderite 1000 panels and baking the panels for 10
minutes at 177.degree. C. One mil dry film thickness paints were made. The
properties of the paint are given as follows:
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 2H
Knoop Hardness 18.4
Direct Impact (lb-in)
80
T-bend (no pick) 4 T
Adhesion 5
MEK Double Rubs 200
Gloss 60.degree. 100
______________________________________
EXAMPLE 9 (Control)
A low VOC paint was made using Rucoflex S-107-210 polyester diol. The
following formulation was used.
______________________________________
Amount (g)
______________________________________
Polyester Diol (Rucoflex .RTM. S-107-210)
35.0
HMMM 17.5
Nacure .RTM. 2500 0.5
Solvent Mix 6.7
Dow Corning .RTM. DC-57
0.1
______________________________________
The resulting paint had a measured VOC content of 1.8 lbs/gal. at a
viscoslity of 21.7 seconds (Zahn #3). A one mil dry film thickness paint
was applied on Bonderite 1000 panels. The panels were cured for 10 minutes
at 177.degree. C. Results are given below:
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness F
Direct Impact (lb-in)
120
T-bend (no pick) 4 T
Adhesion 3
MEK Double Rubs 200
______________________________________
EXAMPLE 10
A paint was made by replacing 20% of the binder in Example 9 with the
reaction product prepared in Example 1. The formulation used was as
follows:
______________________________________
Amount (g)
______________________________________
Polyester Diol (Rucoflex .RTM. S-107-210)
28.0
HMMM 19.0
Ex. 1 Reaction Product
5.0
Nacure 2500 0.5
Solvent mix 7.9
Dow Corning DC-57 0.1
______________________________________
The resulting paint had a measured VOC content of 1.9 lbs/gal. at a
viscosity of 21.9 seconds (Zahn #3). A one mill thick dry film was applied
to Bonderite 1000 panels. The panels were cured for 10 minutes at
177.degree. C. Test results were as follows:
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 3H
Direct Impact (lb-in)
140
T-bend (no pick) 4 T
Adhesion 3
MEK Double Rubs 200
______________________________________
EXAMPLE 11
The polyesterdiol formulation of Example 9 was modified by addition of the
reaction product of Example 2 as follows:
______________________________________
Amount (g)
______________________________________
PE Diol (Rucoflex .RTM. S-107-210)
28.0
Ex. 2 Reaction Product
5.05
HMMM 19.0
Nacure 2500 0.25
57 .RTM. 0.1
Solvent Mix 7.15
______________________________________
The resultant paint had a measured VOC content of 2.1 lbs/gal. and a
viscosity of 22.9 seconds (Zahn #3). One mil dry thickness paint was
applied to Bonderite 1000 panels. The panels were cured for 10 minutes at
177.degree. C. Test results are as follows:
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness H
Direct Impact (lb-in)
140
______________________________________
EXAMPLE 12
The polyester diol formulation of Example 9 was modified by the addition of
the reaction product of Example 3 as follows:
______________________________________
Amount (g)
______________________________________
PE Diol (Rucoflex .RTM. S-107-210)
28.0
HMMM 20.0
Ex. 3 Reaction Product
5.20
Nacure 2500 0.65
DC .RTM. 57 0.10
Solvent Mix 7.20
______________________________________
The resulting paint had a measured VOC content of 1.8 lbs/gal. and a
viscosity of 22.1 seconds (Zahn #3). One mil dry film thickness paint was
applied to Bonderite 1000 panels. The panels were baked for 10 minutes at
177.degree. C. Results are as follows:
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness
H
MEK Double Rubs
100
______________________________________
EXAMPLE 13
The polyester diol formulation of Example 9 was modified by the addition of
the reaction product of Example 4, as follows:
______________________________________
Amount (g)
______________________________________
PE Diol (Rucoflex .RTM. S-107-210)
28.0
HMMM 19.0
Ex. 4 Reaction Product
5.20
Nacure 2500 0.65
DC .RTM. 57 0.10
Solvent Mix 7.35
______________________________________
The resulting paint had a measured VOC content of 1.9 lb/gal. and a
viscosity of 24.8 seconds (Zahn #3). One mil dry film thickness paint was
applied to Bonderite 1000 panels. The panels were baked for 10 minutes at
177.degree. C.
______________________________________
Dry Film Testing
______________________________________
Pencil Hardness 2H
Direct Impact (lb-in)
100
MEK Double Rubs 200
______________________________________
Comparative Example 14
This example which is outside the scope of the present invention
illustrates the preparation of a composition of the type described in
Example 5 of U.S. Pat. No. 5,166,289 wherein neopentyl glycol-bis
para-hydroxybenzoic acid is used as a hardener component.
The paint formulation of Example 9 was modified by inclusion of NPG-bis
PHBA in the composition, as follows:
______________________________________
Millbase Amount (g)
______________________________________
PE Diol (Rucoflex .RTM. S-107-210)
31.5
HMMM 18.0
NPG-bis PHBA 4.0
Nacure 2500 0.32
DC .RTM. 57 0.1
Solvent Mix 8.7
______________________________________
The resulting paint had a VOC content of 2.1 lbs/gal. and a viscosity of
24.8 seconds (Zahn #3). One mil dry film thickness paint was applied to
Bonderite 1000 panels. The panels were baked for 10 minutes at 177.degree.
C. Test results are as follows:
______________________________________
Pencil Hardness 2H
Direct Impact (lb-in)
160
______________________________________
Analysis of the test results of the examples demonstrates that formulations
within the scope of this invention have hardness and impact properties
comparable to those achieved in U.S. Pat. No. 5,166,289 and, at the same
time, may be made from formulations having a lower content of volatile
organic compounds and workable viscosities in the range of about 20-30
Zahn seconds.
The coatings and paints of the invention can be used for spray, roller or
dip application to various metal surfaces such as automotive surfaces,
building panels, metal furniture, appliances and other metal surfaces and
for coil coating applications, followed by suitable baking to provide
hard, durable and decorative finishes.
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